The correct answer is C. 17th.
Halogens are non-metals that are highly reactive and form salts with metals. They are located in Group 17 of the periodic table, which is also known as the halogen group. The halogens are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
Fluorine is the most reactive element in the periodic table. It is a pale yellow gas that is very poisonous. Chlorine is a greenish-yellow gas that is also poisonous. Bromine is a reddish-brown liquid that is also poisonous. Iodine is a purple solid that is less poisonous than the other halogens. Astatine is a radioactive element that is very rare.
The halogens are used in a variety of applications, including:
- Fluorine is used to make refrigerants, bleach, and Teflon.
- Chlorine is used to make bleach, PVC, and insecticides.
- Bromine is used to make flame retardants and photographic chemicals.
- Iodine is used to make antiseptics and iodized salt.
- Astatine is used in research and has no commercial applications.